The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
A variety of materials are often joined together in applications such as automobiles, and more particularly an automotive body to its roof, and are configured to meet specific operational requirements and conditions. Automotive manufacturers are increasingly using advanced materials to reduce weight and thus increase fuel economy. These materials include aluminum, carbon fiber composites, and magnesium, among others. The tailored use of advanced materials for components being joined such as a roof can save significant mass over conventional all steel or all aluminum designs.
In an automotive build process, a finished body is treated to various temperature dependent coating processes, such as electro-coat (e-coat), and the painting process. The high temperatures of this process are also used to cure adhesives used in the vehicle. Materials such as steel and aluminum, and their specific geometric configuration within a part or assembly, will expand at elevated temperatures and at different rates. The “coefficient of thermal expansion” (CTE) is a metric that describes the percentage growth of an object as a function of temperature. The CTE of aluminum is significantly higher than that of steel, which is often much higher than composite materials. Therefore, when heat is applied to the vehicle, a steel part, such as a body side would expand less than an aluminum part, such as a roof panel. This can cause distortion in the final assembled geometry, which can then result in unacceptable fit to the vehicle body, as well as residual stresses.
Typical assembly configurations for automotive components include mechanical joints such as self-piercing rivets (SPRs) used in conjunction with an adhesive. During thermal processing, these mechanical joints may act as pins and restrict part movement, which can lead to yielding of one or more parts of an assembly as the different parts expand and contract at different rates. Using adhesive alone may not be acceptable in high volume production as the parts often are “geometry set” prior to entering paint ovens where the adhesive is cured and locked into place. This “geo-setting” process is used to establish good fit to the vehicle body.
These assembly issues, among other mechanical joining issues, are addressed by the present disclosure.